Semiconductor switching arrangement with device using depletion layer to interrupt current path



INK EJWI? RANGEMENT WITH DEVICE USING LAYER T ERRUPT CURRENT PATH Feb. 9, R965 0. w. MEMEL SEMICONDUCTOR SWITCHING DEPLETI Filed Ma 3 2 l/cs bs v00 Vcs v00 INVENTOR OSCAR WILLEM MEMELINK BY 3,169,197 SEMECONDUCTOR SWETCHING ARRANQEMENT WITH DEVICE USKNG DEPLETiON LAYER T INTERRUPT CURRENT PATH Oscar Willem Merneiinlr, Eindhovcn, Netheriands, assignor to North American Phiiips Company, lino, New York, N.Y., a corporation of Delaware Filed Mar. 17, 1960, Ser. No. 15,692 Claims priority, application Netherlands, Apr. 28, 1959, 238,689 4 Claims. (Cl. 30788.)

This invention relates to devices comprising a semiconductive body with 2 diode structure constituted by two electrodes of different types with an interposed highresistance layer, together with a further rectifying e1ectrode referred to as the control electrode the depletion layer of which can interrupt the current path in the diode structure from the electrode of differing type from the control electrode, referred to as the surge electrode, to the electrode of corresponding type to the control electrode, referred to as the base electrode, without bringing about punch-through to the base. A semi-conductive electrode system of this kind is described in my prior copending application, Serial No. 792,902, filed February 12, 1959, now Patent No. 3,081,404, of which the present application is a continuation-in-part.

An object of the invention is to provide a device which can be used as an electronic switch. In my aforementioned prior application, devices were already described for such a use which is based on the fact that a negative resistance occurs due to the current flowing to the control electrode in the sense that a resistor included in the control-electrode circuit brings about positive feedback. An object of the invention is to provide a variant of such a device which is characterized in that only a very low control voltage and control energy sutfices for bringing about a switching action.

The invention is characterized in that the base electrode and the surge electrode are included between two conductors which can be connected together in a conductive manner by the control of the current-voltage relationship with breakdown characteristic and adjoining negative resistance portion as obtained between the base and the surge electrode by the action of a low cut-off potential active between the control electrode and the surge electrode, for example the contact potential, between the control electrode and the electrode itself.

According to the invention, in contradistinction to the embodiments described in my prior application, in which a constant biasing potential between the control electrode and the base was provided, a low potential is normally active in the blocking direction between the control electrode and the surge electrode. This results in a depletion layer penetrating the semi-conductor body from the control electrode and cutting off the current path between the surge electrode and the base, similarly to what has been described in my aforementioned application. In the new switching arrangement, the voltage between the base and the surge electrode is increased while maintaining constancy of the potential in the cut-off direction between the control electrode and the surge electrode, in the sense that the base is polarised more negatively if it is of the n-conductivity type, and polarised more positively if it is of the p-conductivity type, until break through oficurrent from the base to the surge electrode takes place. This breakthrough of current is to be regarded as a. local pene tration of the depletion layer. After the current has broken through, a great current can flow between thebase and the surge electrode at the expense of a low potential between these two electrodes, since these electrodes, together with the semi-conductor body, constitute in this 3169i?! Patented Feb. 9, W65

state a p-i-n diode structure polarised in the forward direction.

A feature of a device according to the invention is the low cut-off voltage between the control electrode and the surge electrode which is required for bringing about breakthrough of the current between the base and the surge electrode at a high voltage.

It will be evident that an increase in the cut-off voltage between the control electrode and the surge electrode gives rise to an increase of the striking voltage between the base and the surge electrode. Conversely, a decrease of the cut-off voltage between the control electrode and the surge electrode gives rise to a decrease of the striking voltage between the base and the surge electrode. It has been found that, even if an external blocking-voltage source is omitted between the control electrode and the surge electrode and hence these electrodes are short-circuited, a striking voltage subsists, since the inner contact potential differs between the control electrode and the surge electrode is sufiicient for obtaining a depletion layer which cuts off the current path between the base and the surge electrode.

In order that the invention may be readily carried into effect, it will now be described in detail, by way of example, with reference to the accompanying drawing, in which:

FIG. 1 shows a schematic diagram of one embodiment according to the invention.

FIG. 2 shows current-voltage characteristics between the surge electrode and the base for different values of the voltage at the control electrode, and FIG. 3 shows the relationship between the striking voltage in the characteristic of FIG. 2 and the voltage between the control electrode and the surge electrode.

FIG. 4 is a circuit diagram of a sawtooth generator in which the invention is applied.

Referring now to FIG. 1, a semi-conductor body 1, preferably of disc-shaped form, comprises a monocrystal of substantially intrinsic conductivity. The difference in the content of active donor impurities and active acceptor impurities in this high-ohmic intrinsic part is, in absolute value, less than 5x10 per cm. and preferably less than 10 per cm. Alloyed in opposition on the body 1 are two electrodes of opposite types, namely the control electrode comprising a contact 2 and the associated lowohmic n-type zone 3, and the surge electrode comprising a metallic contact 4 and the associated low-ohmic p-type zone 5. Provided along the periphery of the circular symmetrical semi-conductive body 1 is the base electrode comprising an annular metal contact 6 and the associated annular low-ohmic n-type zone 7. The base (6, 7) constitutes, together with the surge electrode (4, 5) a p-i-n diode structure of this semi-conductive electrode system. The annular shape of the base is not essential to the operation but is preferably used in connection with the further improvement of the diode characteristic which can thus be obtained. By the use of intrinsically semiconductive germanium in the body 1, all three doped electrodes constitute rectifying connections with the body. However, for the operation according to the invention, there is only the primary condition that the control electrode shall constitute a rectifying connection. Since the base and the control electrode are of corresponding type, the base, too, is always a more or less rectifying connection. This requirement by no means exists for the surge electrode.

As an example a germanium body with an impurity conent of 5X10 acceptors per cm. may be employed.

The contacts 2 and 4 may be of 98% bismuth, 2% arsenic and 99 /z% indium, /a% gallium, respectively, alloyed to the crystal at 650 C. and 600 C. respectively for about 10 minutes each. The zones 3 and 5 may be spaced apart by 30 microns. A suitable low ohmic zone 7 may be made by alloying at 550 C. a ring 6 composed of 95% indium and 5% arsenic to the crystal. For further details on the manufacture and use of such a device, see my aforementioned prior application, Serial No. 792,902, especially pages 25 and 26 thereof.

According to the invention, the surge electrode 4, instead of the base contact 6, is connected to earth or another point of constant potential, while the diode structure formed between the base 6 and the surge electrode 4 is used as an electronic switch. Upon increasing voltage V between these electrodes the current I flowing to the base 6 initially increased only to a slight extent, but subsequently, when the striking voltage V is exceeded, suddenly increases to a very high value.

FIG. 2 shows these striking characteristics. Curve a applies for an external voltage V of volt between the control electrode and the surge electrode (2 and 4, respectively), which means that only the contact potential between the electrodes is active in the circuit. Curve b applies to a voltage V of 0.2 volt and curve 0 to a voltage V. of 0.5 volt. Curve d applies to arbitrary negative values for the voltage V From this it follows that a very effective blocking of the current path between the base and the surge electrode (6 and 4 respectively) may be brought about even for a very low value of the volatge V The base voltage V must then exceed the striking voltage V in order to close the current path to the surge electrode.

FIG. 3 shows in what manner the striking voltage V increases upon increasing positive value of the control voltage V A low negative value of the control voltage V already suffices for readily closing the current path between base and surge electrodes (curve d in FIG. 2). If a resistor 8 is connected between the control electrode and the surge electrode (2 and 4 respectively) the blocking the path between electrodes 4 and 6 is detrimentally affected since the leakage current flowing through this resistor 8 (approx. 100 ,ua.) decreases the cut-off voltage which is actually active between the control electrode and the surge electrode (2 and 4 respectively). On the other hand, the resistor 8 brings about a decrease in the current to the control electrode 2 in the on-state (current-conveying state between the electrodes 4 and 6) of the semi-conductive element and may for this reason be desirable in certain cases. Such a resistor therefore preferably has a value higher than the internal resistance of the diode structure between the base and the surge electrode in the good current-conveying state, but lower than the leakage resistance between the control electrode and the two other electrodes in the poor current-conducting state of the semi-conductor element, the resistor preferably having a value between 100 and 2000 ohms if the element 1 is made of germanium.

The current-voltage characteristic obtained between the electrodes 6 and 4 (FIG. 2) is used to operate the device as an electronic switch. In order to bring about a conductive connection between conductors 9 and 1t connected to the electrodes 6 and 4, either these conductors have momentarily applied to them a voltage V which exceeds the striking voltage V (FIG. 2) or the voltage V is momentarily decreased so as to obtain a point of adjustment in the relevant portion of the characteristic in FIG. 2, for which a low voltage drop (0.5 volt) at high current strength (at least several milliamps) applies. The connection is interrupted again by momentarily making the voltage on and/or the current through the conductors 9, 10 equal to zero. In other words, the device is pulsed to switch it from the Off to the On state, and similarly pulsed to switch it back to the Off state. It is therefore a bistable switch.

Preferably, a biasing potential of several volts, for instance 10 volts, is applied to the conductors 9, 10. With a small positive value of the voltage at the control 7 between the conductors 9, 10 can never exceed this striking voltage V A low voltage of 0.5 volt at the control electrode is already sufiicient for bringing about a threshold voltage of about 70 volts. If, however, the voltage at the control electrode 2 becomes of opposite polarit then owing to the negative resistance portion of the characteristics shown in FIG. 2, a state of high current conductivity and low Voltage drop is obtained which switches on the path between conductors 9 and 10 automatically. The control voltage and control energy required at the control electrode to obtain this operation is extremely low, since only a few tenths of 21 volt suffice.

In one practical embodiment when using a switching voltage V of a bias value of 0.2 volt and a biasing potential of 20 volts between the conductors 9 and 19 it was possible to switch a power of 200 milliwatts (20 volts X10 ma.) between the conductors 9, 1d. The switching energy required therefore was even less than 1 W. sec.; the current flowing through the control-electrode circuit during the on state was limited to 0.5 ma. by means of a resistor 8 of 400 ohms. This current may, if desired, be reduced substantially to zero by switching over the switching voltage V from a low positive value to a permanent low negative value.

It will be evident that all kinds of variants are possible, as already referred to in my aforementioned application. Notably the shape and the conductivity types of the various electrodes as specified therein may still be varied.

It is fundamentally conceivable to connect the control electrode to a point of defined potential and to apply the switching voltage to the surge electrode. The differential resistance of the diode structure between the base and the control electrode is comparatively high, however, which is mostly objectionable for the envisaged purpose. In addition, the current to the surge electrode cannot be suppressed by a resistor in a similar manner, since then the current to the control electrode is also suppressed.

FIG. 4 shows a sawtooth-generator in which a condenser 15 is connected to the main supply through a resistor 16 to provide a constant current loading circuit of said condenser 15. The condenser 15 may have a value of 10,000 pf. and the resistor of 10 Kt while the supply voltage may be v. The semi-conductive system according to FIG. 1 is connected with its terminals 9-10 to said condenser 15. The surge electrode 4 is connected to ground and the base electrode 6 is connected to the junction of condenser 15 and resistor 16. A bias voltage-source 17 of about 1 v. is connected, in series with a resistor 18 of about 1 K9, between the surgeand control electrodes and sufiices to block the current flow between electrodes 4 and 6. Input pulses 19 of about 1 v. and a duration of about 10 ,usec. are supplied, through blocking condenser 20 of about 10,000 pf., to the control electrode 2, with the result that the path between electrodes 4 and 6 becomes alternately conductive as a consequence of which the voltage generated across the condenser 15 becomes a sawtooth shape with a steep rising flank of about 5 #566. risetime. The repetition frequency may be for instance 14 kc./scc.

What is claimed is:

1. A circuit arrangement comprising a semi-conductor device including a high-resistance semi-conductive body, two spaced electrode connections of opposite-type conductivities to said body and defining with the intervening body portions a diode current path, a rectifying connection to said body and positioned so that when biased in the reverse direction, a depletion region is formed in said body originating at said rectifying connection and interrupting the said diode current path before punching-through to that one electrode of the said two electrodes whose conductivity-type is equivalent to said rectifying connection, means connected to the other electrode of the saidtwo electrodes for. maintaining it at a fixed potential at all times, means providing a voltage difference between the said other electrode and the said rectifying connection which biases the latter in the reverse direction thereby interrupting the diode current path, and means establishing a-voltage difference between the said two electrodes including avoltage value above their breakdown voltage.

2. An arrangement as set forth in claim 1 wherein the means providing a voltage difference between the said other electrode and the rectifying connection is their interconnection providing a contact potential difierence.

3. A circuit arrangement comprising a semi-conductor device including a high-resistance semi-conductive body, two spaced electrode connections of opposite-type conductivities to said body and defining with the intervening body portions a diode current path, a rectifying connection to said body and positioned so that, when biased in the reverse direction, a depletion region is formed in said body originating at said rectifying connection and interrupting the said diode current path before punching-through to that one electrode of the said two electrodes whose conductivity-type is equivalent to said rectifying connection, means connected to the other'electr-ode of the said two electrodes for maintaining it at ground potential, means providing a voltage difference between the said other electrode and the said rectifying connection which biases the latter in the reverse direction thereby interrupting the diode current path, means establishing a voltage difference between the said two electrodes below their breakdown voltage, and means for momentarily reducing the voltage difference between the said other electrode and the said rectifying connection causing a high current flow along the diode current path.

'4. An arrangement as set forth in claim 3 wherein a resistor is connected between the said rectifying connection and the said other electrode, said resistor having a resistance which is between (a) the resistance of the body portions of the diode current path when high current flows, and (b) the leakage resistance between the rectifying connection and the other two electrodes when the diode current path is interrupted.

References Cited in the file of this patent UNITED STATES PATENTS 2,862,117 Mathis Aug. 6, 1957 2,863,056 Pankove Dec. 2, 1958 2,922,897 Maupin Jan. 26, 1960 2,959,681 Noyce Nov. 8, 1960 UNITED STATES PATENT OFFICE Patent No. 3,169,197

February 9, 1965 Oscar Willem Memelink It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below Column 2, line 19, for "differs" read difference line 68 for-=Lconenfl" read content column 3, line 28, for "volatge" read vol-cage Signed and sealed this 6th day of July 1965.

(SEAL) Attest:

ERNEST Wu SWIDER EDWARD J. BRENNER At testing Officer (lommissioner of Patents 

1. A CIRCUIT ARRANGEMENT COMPRISING A SEMI-CONDUCTOR DEVICE INCLUDING A HIGH-RESISTANCE SEMI-CONDUCTIVE BODY, TWO SPACED ELECTRODE CONNECTIONS OF OPPOSITE-TYPE CONDUCTIVITIES TO SAID BODY AND DEFINING WITH THE INTERVENING BODY PORTIONS A DIODE CURRENT PATH, A RECTIFYING CONNECTION TO SAID BODY AND POSITIONED SO THAT WHEN BIASED IN THE REVERSE DIRECTION, A DEPLETION REGION IS FORMED IN SAID BODY ORIGINATING AT SAID RECTIFYING CONNECTION AND INTERRUPTING THE SAID DIODE CURRENT PATH BEFORE PUNCHING-THROUGH TO THAT ONE ELECTRODE OF THE SAID TWO ELECTRODES WHOSE CONDUCTIVITY-TYPE IS EQUIVALENT TO SAID REC- 